A lattice filter model with accurate lip impedance for dynamic articuratory movement

In the vocal tract model, the area function of vocal tracts is accurately represented by a polynomial function with only a few parameters, and the digital filter realization includes the loss, the accurate lip impedance and the variation of the tract length. We measured the lip impedance using a manikin and pipes set in a baffle, and obtained the reflection coefficient at the lips. From the results of these experiments, we discuss the difference between the measured characteristics and those of a spherical baffle model, and show a method to obtain approximate digital filters for the reflection characteristics at the end of the vocal-tract; i.e. the lips. By introducing this filter, it becomes possible to express arbitrary changes of the length of the vocal-tract without changing the sampling frequency.